GREENLIFE MAT­TERS

Nurs­eries, gar­den cen­tres and home gar­den­ers have been com­mended for their ef­forts in the fight against myr­tle rust dis­ease. As the weather warms up in spring, this se­ri­ous dis­ease will be on the move again and we must re­main vig­i­lant.

Go Gardening - - Editorial -

Sav­ing our trees

In this win­ter’s Go Gar­den­ing mag­a­zine (May 1) we an­nounced that myr­tle rust had ar­rived on Raoul Is­land, 1000km north­east of the North Is­land. Main­land New Zealan­ders were be­ing asked to be on vig­i­lant watch for the se­ri­ous wind borne dis­ease threat­en­ing some of our most pre­cious trees. By the time the mag­a­zine was printed a few days later, myr­tle rust had been found in North­land.

Early in May New Zealand Plant Pro­duc­ers In­cor­po­rated (NZPPI) pro­vided nurs­eries, trans­porters and gar­den cen­tres with guide­lines to man­age the risk of dis­tribut­ing or be­com­ing in­fected with myr­tle rust. Af­ter the first de­tec­tion of myr­tle rust in north Taranaki on May 12, Ministry for Pri­mary In­dus­tries (MPI) en­dorsed those guide­lines and praised the nurs­ery in­dus­try for its vig­i­lance. An­drew Har­ri­son, chair­man of NZPPI called it a “call to arms for our in­dus­try”.

De­spite those in­volved do­ing ex­actly the right thing, by June 1 we had 32 con­firmed myr­tle rust finds. The list of in­fected sites con­tin­ued to grow and by mid-July, the count of con­firmed sight­ings was up over 90. The ma­jor­ity of th­ese were in pri­vate gar­dens. So far, the most af­fected species in New Zealand are ra­ma­rama and po­hutukawa, but other myr­tle fam­ily mem­bers such as manuka and fei­joa are still at risk.

Win­ter has bought sci­en­tists a lit­tle time. The fun­gus hi­ber­nates in cold tem­per­a­tures, so even though the weather has been windy, there are few spores pro­duced for spread­ing. But as the weather warms up the fun­gus starts re­leas­ing a whole new gen­er­a­tion of vir­u­lent spores, so tiny and light that they are car­ried long dis­tances on the wind. When they land on a sus­cep­ti­ble host they ger­mi­nate, grow through the leaf tis­sue and form a network of tiny branches called hy­phae, which in turn pro­duce a new crop of spores. Come spring, plant pro­duc­ers and re­tail­ers will be at the fore­front of the ef­fort to de­ter­mine ex­actly where the dis­ease is present and the scale of the out­break.

Since myr­tle rust first ap­peared in May, the fo­cus of the re­sponse has been on ag­gres­sive con­tain­ment and erad­i­ca­tion. Grow­ers and re­tail­ers who are mem­bers of NZPPI are work­ing to strict pro­to­cols to en­sure the plants ar­riv­ing in gar­den cen­tres are highly un­likely to be car­ry­ing spores of myr­tle rust.

Myr­tle rust spores are so tiny and light that they’re car­rried long dis­tances by wind.

As time goes on, we are likely to be fac­ing the re­al­ity that this dis­ease can­not be erad­i­cated com­pletely and we will have to find ways to min­imise its ef­fect. NZPPI and MPI are work­ing closely to­gether on con­tin­gency plans to pre­pare for long term man­age­ment of myr­tle rust.

WHAT IS MYR­TLE RUST?

Myr­tle rust is a fun­gal dis­ease na­tive to South Amer­ica. It is caused by the par­a­sitic fun­gus Aus­trop­uc­cinia psidii which at­tacks plants of the myr­tle fam­ily (myr­taceae).

WHAT DOES MYR­TLE RUST LOOK LIKE?

Myr­tle rust at­tacks young, soft, ac­tively grow­ing leaves, shoots and young stems. It is some­times found in flowers and fruit. Pow­dery, bright yel­low or orange ‘pus­tules’ are the first symp­toms to ap­pear. As the dis­ease pro­gresses the de­vel­op­ing le­sions may cause a de­for­ma­tion of leaves and shoots, twig dieback and, in se­vere cases, the death of the en­tire plant.

HOW DOES MYR­TLE RUST SPREAD?

Myr­tle rust spores are car­ried large dis­tances by wind. Spores are also spread by in­sects and rain splashes, and can be trans­ported on cloth­ing, ve­hi­cles or equip­ment. Early de­tec­tion is key in pre­vent­ing its spread.

WHICH PLANTS ARE AF­FECTED?

Myr­tle rust at­tacks mem­bers of the myr­taceae fam­ily, which in­cludes: po­hutukawa, manuka, kanuka, ra­ma­rama ( Lophomyr­tus), gum trees ( Eu­ca­lyp­tus), bot­tle­brush, pep­per­mint myr­tle ( Ago­nis), fei­joa, guava ( Psid­ium), Chilean guava or ‘NZ cran­berry’ ( Myr­tus ugni).

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